The present invention relates generally to a method of building miter gates within a lock and dam system and more particularly to a method of construction that reduces the rate of structural fatigue associated with use of the miter gates within the lock and dam system.
1. Status of the Art
Miter gates have been in use throughout the United States for a number of years. Typically made of steel, these gates within the lock and dam systems, provide ways for boat and barge traffic to safely navigate controlled water ways.
A controlled water way, such as the Mississippi river, may have several lock and dam systems along its route. When in a locked position, the system blocks water upstream from flowing downstream and thus allows a controller, such as the Army Corp of Engineers, to raise and lower the water level as required. After proper adjustment, the system can be opened to allow for water traffic to pass.
After all traffic has cleared, the miter gate system is closed. Closing the system requires a great deal of force. The closing process ends with a great amount of stress being applied to the end of the miter gate system during the closing impact. This stress is transferred from the closing or miter end, to the pivot or quoin end of the system.
Traditionally, a miter gate is composed of a series of diaphragms supported by network of girders, stiffeners and other support members. When the closing impact occurs, the impact stress must be absorbed at the miter end, transferred down the network of girders and dissipated in the ground at the quoin end. The initial impact forces are currently absorbed by the cross-sectional area of a series of vertical thrust plates and the horizontal web plates they are secured between. Because the thrust plates are secured to the web plates in sections and welded in place to the web plates using a T-joint weld, the stress tends to flow into the web plates creating destructive strains.
Because the miter gate will go through many opening and closing operations during its useful life, the resultant cyclical loading strains in the web plates causes linear cracking over time. The cracking, or laminar tearing, detrimentally affects the useful life of the miter gate system. There is therefore a need for a method of making a miter gate system that will reduce the destructive cracking resulting from the strains associated with the closing impact.
A common method of reducing strain is to pre-stress materials. Pre-stressing the thrust plate, web plate and girder structures of a miter gate system would require pre-heating the structures, particularly their joining sections, to approximately the welding temperature and then slowly cooling the pieces. Not only would extensive pre-stressing add significantly to the construction costs, but because of the large sizes associated with nearly every miter gate system, such a pre-stressing process would also add significantly to the time needed for construction. Therefore, there is a need for a method of constructing the miter gate system which reduces destructive cracking in a cost effective and timely manner.
2. Features of the Invention
A general feature of the present invention is the provision of a method of constructing a miter gate system which overcomes the problems found in the prior art.
Another feature of the present invention is the provision of a method of constructing a miter gate system which prolongs the useful life of the system.
A further feature of the present invention is the provision of a method of constructing a miter gate system which reduces closing impact related cracking.
A still further feature of the present invention is the provision of a method of constructing a miter gate system which is cost-effective.
Another feature of the present invention is the provision of a method of constructing a miter gate system which keeps construction time reasonable.
These, as well as other features and advantages of the present invention, will become apparent from the following specification and claims.